SPATIO-TEMPORAL CHARACTERISTICS OF MIOCENE SILICIC MAGMATISM ACROSS NORTHEASTERN NEVADA: LINKS BETWEEN MAGMATISM AND EXTENSION, NOT THE YELLOWSTONE HOTSPOT

In northeastern Nevada, new geochemical, chronologic, and field constraints, coupled with prior geological mapping, indicates that 16.1 to 15.0 Ma Jarbidge Rhyolite volcanism occurred with spatially and temporally coincident lithospheric extension. The Jarbidge Rhyolite is quartz-phyric and crops out as lavas and domes from the area around Jarbidge, Nevada east to the NV-UT-ID tristate region. Here, we report new laser ⁴⁰Ar/³⁹Ar age for sanidine from lavas either mapped as, or that texturally resemble, the Jarbidge Rhyolite. One sample was collected from a lava-dome complex adjacent to the Ruby-East Humboldt Range (near Wells, NV) and yields an age of 15.3 ± 0.04 Ma. Another sample was collected from a lava-dome complex just west of West Wendover, NV and yields a 13.7 ± 0.03 Ma age. Results are pending for other Jarbidge Rhyolite lavas that crop out in northeast Nevada near the Utah and Idaho borders (e.g., Little Goose Creek region), but based on a 13.6 Ma ⁴⁰Ar/³⁹Ar age on a crystal-poor rhyolite lava in close proximity to these Jarbidge Rhyolite units, we expect similar ~14-13 Ma ages. These results confirm prior, limited, K-Ar ages from silicic lavas in the region that coupled with the 16.1 to 15.0 Ma ages from the most voluminous exposures of Jarbidge Rhyolite in Nevada, verify that Miocene silicic magmatism (including the Jarbidge Rhyolite) has migrated eastward across northeastern Nevada since the mid-Miocene. Furthermore, this migration, seems to be coupled to a previously documented eastward migration of extensional basin formation and also pre-dates caldera-forming silicic volcanism on the Snake River plain at any given longitude by 2 to 4 m.y. These relationships are difficult to explain if northeastern Nevada Miocene silicic volcanism, including the Jarbidge Rhyolite, is attributed to the influence of a lower mantle plume. Thus we suggest that rapid Miocene extension across northeastern Nevada caused small volume silicic magma generation, and eruption. This is supported by chemical and isotope constraints on the Jarbidge Rhyolite, which imply a substantial involvement of Archean lithosphere, including quartzofeldspathic crust. We attribute the extensional collapse of the Mesozoic Nevadaplano high elevation plateau as the primary driving factor in the magmatism and extension, not the Yellowstone hotspot.